Remember if you lock your twitter account (safe mode) your tweets won't be public. That is they won't appear in twitter search or Google search engine or anywhere else. They will be only readable by your followers. Your followers will not be able to use the retweet feature on your updates (the button for it will not appear in their Home's). It is better for businesses to conduct their tweeting with open accounts. You can set up a separate locked account for what you would consider private if you like.